1. Field of the Invention
The present invention refers to a process for the manufacture of reflecting glass, particularly suited for use in the field of vehicles as a rear view mirror and/or side window and in the field of building construction for external glazing and/or non-opaque mirrors.
The present invention also refers to a reflecting glass obtained using said process.
2. Description of the Prior Art
Methods of manufacture of sheets of glass capable of being advantageously employed in the above mentioned fields and for the applications specified are known in the state of the art.
In general a glass made by said methods, at wavelengths comprised between 350 nm and 750 nm reflects a rate from 20% to 50% of the incident light in a perpendicular direction, and transmits, at the same wavelengths, a rate from 15% to 70% of the incident light.
Most recent are methods teaching a glass with those characteristics is produced by coating the surface of the glass to be in contact with the external environment, with at least one layer of dielectric material (in general a metal oxide).
The coating is obtained using the known method of vacuum cathodic sputtering, hereinafter called physical deposition, or using another known method consisting in the immersion of the glass in various chemical solutions, and successively the promotion of precipitation onto said glass of chemical substances, which method will hereinafter be called chemical deposition.
The product obtained according to the manufacturing methods mentioned hereinabove has several drawbacks: the coating is, in fact, exposed during its working life to atmospheric agents, as the deposition is carried out on the outer surface of the glass, and this causes deterioration and wear. In particular, in the case of deposition of layers using the physical method, the coating, while showing a resistance and endurance in line with the user specifications prescribed by the authorities of the USA and the EEC, has a shorter life than that produced using the chemical method.
On the other hand, the latter method is more expensive than the physical one, due to the complexity of its realization.
There is furthermore known in the state of the art, and this forms the object of European published patent application number 0318440, a process for changing the refraction index value in one or more layers of a sheet of glass, consisting in a suitable use of the ionic implantation method.
This method permits the formation of a homogeneous and continuous layer of a substance under the surface of the glass, by inserting into the molecular structure of the glass itself the ions of a selected element, at selected chosen conditions of glass temperature and ion dosages.
In particular, in the cited patent application, the ions of the elements argon, xenon, krypton, neon, helium, nitrogen or carbon were chosen which, when inserted into the molecular structure of the glass, at a certain depth, vary the refraction index of the same.
The use of this process gives the reflecting glass characteristics of notable duration and resistance to atmospheric agents, as the implanted layer is buried within the glass itself.